Electrical systems with packaged electrical and electronic components are known and are in use. For example, Motor Control Centers (MCC's) are used for power and data distribution in large and industrial operations. In MCC's, a variety of components, such as switchgear, semiconductor power electronic circuits, programmable logic controllers, motor controllers, and so forth, are housed in large electrical enclosures that may be subdivided into sections or columns, which may be further subdivided into compartments. The MCC includes associated bus bars, interconnections and supporting structures for distribution of electrical power to the various compartments.
Typically, the MCC is connected to a main power line that may feed three-phase AC power to horizontal bus bars of the MCC. The horizontal bus bars, in turn, may feed the three-phase power to vertical bus bars disposed in each of the sections or columns of the MCC. The vertical bus bars, in turn, may feed the three-phase power to various electrical units (which typically include electrical components) that are installed in compartments of a section. The electrical units, in turn, may provide power terminals (conductors), such as copper bus bars, for feeding the three-phase power to a system environment, such as motors, as may be required for various applications.
It is often desirable to partially disconnect such electrical units them from the MCC from time to time to perform testing or other diagnostics. A partial disconnection typically means partially withdrawing the electrical unit from the MCC, such that the three-phase power is no longer provided to the electrical unit, but communications and control signals remain connected to the electrical unit. This provides an advantageous state for testing communications and control of electrical components with reduced risk of inadvertently delivering three-phase power. However, partially withdrawing an electrical unit creates gaps between the electrical unit and the MCC, thereby exposing an operator to a potential risk in the event of an arc fault. It is possible to keep the electrical unit fully inserted while moving an interior portion of the electrical unit to provide the partially disconnected state. However, this requires a smaller overall footprint for the interior portion of the electrical unit, thereby limiting the range of electrical components which could be used. A need therefore exists for an improved electrical unit which mitigates one or more of the foregoing disadvantages.